Jessica (aka Jessie) is a member of Team Rocket. She tends to be a drama queen and has a diabolical temperment. She works with James and Meowth. Their main goal is to steal Pokémon, preferably Ash Ketchum's Pikachu. She and James have rivals Butch and Cassidy. Jessie's name is sometimes spelled as Jesse, as her name comes from the infamous outlaw Jesse James.
Jessie was a poor girl with a cold past whose mother, Miyamoto, disappeared in an avalanche on an expedition of Team Rocket to capture the legendary Pokémon Mew, where unlike her daughter she was very high ranked. As a child, her foster mother (her real mother in the dub) cooked with a "base ingredient," the snow. So, Jessie enjoys eating snow. She would even go out of her way to get some and make some of her mother's old "recipes." She met her mother one last time before she left her in Best Wishes to look for a Celebi. In Best Wishes, she loses some weight due to her promotion in Team Rocket's rankings.
Not much is known about Jessie's past. In the chapter nine of the first season, Jessie talks about her bad memories of study in the Pokémon Technical Institute. At the time, she already knew James; they studied together for "a big test", but after getting the lowest grades in the school's history, they joined a bike gang in Sunny Town episodes later. Jessie went to Team Rocket after failing in her attempt to become a Pokémon nurse, partly due to the fact that the Pokémon nursing school she attended was only for Pokémon who wanted to be nurses (in this case, the Chansey), not for people. But she did not know that until graduation day.
More recently, it was learned that she was studying dance at a school with two friends, letting go of one of her first youthful loves in order to pursue her dream of being a star. However, she failed the test of dance and regrets not having accepted the invitation to accompany the boy to compete in Pokémon Contests. Not much is known of her former love life, but she said that has never been very lucky in love as her grooms have either treated her unfairly and/or abandoned her. She is later paired up with James, a rebellious rich-boy who doesn't want to follow his family wishes, and Meowth, a fast talking Pokémon who has dreams of being on top.
As of her, James' and Meowth's promotion and transfer to Unova, Jessie has become a highly skilled stealth artist, an excellent athlete and is often successful in many missions with her team mates to the point of the trio becoming a serious enemy for Ash and co. The trio were key in Team Rocket's Meteorite plan, taking orders directly from Giovanni himself as well as his secretary. Jessie and her team-mates worked together with Pierce and met Doctor Zager.
Once the plan culminated, Jessie and her team-mates were asked to do as they please in Unova, so they continued working hard to do Team Rocket good and now worked closely with Zager. Ash had thus become less important to them but they would still antagonize him if he interfered in their plans.
In the games, Jessie and James are supposed to be the same age as Ash. However, according to a special CD available only in Japan, Jessie and James are in their 20's in the second episode of Anime. An episode of the season Master Quest, reveals an old woman who is 120 years old Jessie. Jessie amazed at the replica which is 10 times her age. As Jessie obviously has more than 12 years, Meowth asked her where she learned mathematics. She has a long going rivalry with fellow Team Rocket Member Cassidy.
In the episode "The Ultimate Test," while filling out an application she says aloud, "Age: 17, Profession: Diva." She was in disguise and therefore is probably lying about her age (as one should expect she would), but we can at least assume she would not claim to be older than she is because that would go against her character.
In Hoenn, Jessie began to compete as a Pokémon Coordinator, and although she was not successful, she continued to participate in each Pokémon Contest she could. At each contest, she disguised herself due to the notoriety of Team Rocket as a whole. Initially, she cheated, using technological assistance and intervention of James and Meowth, but then began to compete fairly. She often borrowed Pokémon from James for the contests, and has repeatedly used Meowth as one of her Pokémon. Despite losing in all contests in which she participated in Kanto and Hoenn, in the Sinnoh region, she won three ribbons herself, using her Dustox, Yanmega and Seviper, and obtained a ribbon after James won a contest in her place, as well as receiving one from Princess Salvia after she lost to her. Jessie then became eligible to participate in the Sinnoh Grand Festival, and made it to the semi-finals, but lost to Dawn. She also participated in Summer Camp Pokémon and got a diploma/credit for having studied (she was disguised Jessilina). Jessie was the leader of her ragtag group, and she was not afraid to show it. After the Sinnoh Grand Festival, Jessie abandoned the Jessilina alias.
In DP 102 while Ash was fighting Fantina, Jessie is seen participating in a Pokémon Contest in which she won with her Yanmega.
Lilypad Town Ribbon
In DP 146 Jessie was very sick so James disguised himself Jesselina was presented with Meowth and were won the contest after Carnivine winning over a Tyrogue (after having defeated Dawn's Mamoswine in the Semi-Final).
Neighborly Town Ribbon
In DP 167 Jessie competed in a contest in which Johanna (Dawn's mother) was a judge.
Arrowroot Town Ribbon
In DP 171 Jessie lost in the contest. Princess Salvia, disguised as Dawn, gave her the ribbon for the performance she gave during their battle in the Final round.
Grand Festival ranking
Jessie placed in the following Grand Festival competitions:
Jessie caught Seviper after beating him for "eating" Jessie's hair, which enraged Seviper as well as Jessie. He knows the moves Poison Tail, Bite, Wrap and Haze. It has been used in many contests but never won. It is also the main Pokémon Jessie uses for battles in Sinnoh and Hoenn.
Jessie captured Yanmega as a Yanma after another trainer weaken it first. Yanma evolved soon after being caught while in a battle against Ash and his friends in DP080. Jessie used Yanmega in many battles and contests. In the episode "Where No Togepi Has Gone Before!", she is the only Pokémon present not effected by the evil female Togepi's Attract (due to Attract not effecting Pokémon of the same gender) and Jessie reveals she was unaware Yanmega was female until Brock pointed it out. Yanmega knows Silver Wind, AncientPower, Steel Wing and SonicBoom and these make her a strong weapon for Team Rocket.
This Ekans was a birthday gift and was her most beloved Pokémon. It accompanied Jessie from the beginning of the anime. Eventually it evolves into an Arbok because Jessie wished desperately for it to. It is released to protect a group of Ekans in A Poached Ego. It knew Poison Sting, Headbutt, Wrap and Dig.
Jessie captured Dustox as a Wurmple under the belief that it would evolve into a Beautifly. She captured Wurmple at the same time as May caught her's. After a battle against May, it evolved into a Cascoon, not a Silcoon. It later evolved and became one of Jessie's most cherished Pokémon. Jessie later released her to go with a shiny Dustox to make a family and be happy.
Jessie captured Lickitung in Princess Vs. Princess, in the same episode Jessie used it in the Princess Festival and was defeated by Misty's Psyduck. After accidentally exchanging it for Wobbuffet, it was never seen again.
Jessie and this Chansey met at a medical school where Chansey learn to become Pokémon nurses. They both studied together at the school, but unfortunately Jessie couldn't pass because she was human, and the school was meant for Pokémon. Jessie and the Chansey part ways, but Chansey left Jessie with a broken piece of her graduation necklace. Jessie is reunited with this Chansey many years later, when she is in team rocket in the episode Ignorance is Blissey. She recognizes the broken graduation necklace, and is thrilled to find that her old friend has evolved into a Blissey, and realized her dream of being a Pokémon nurse. This Blissey tends to get a little over-excited when it comes to aiding people, usually spilling what it is carrying or something of the sort, but it's intentions are for good.
Rhydon is one of the Giovanni's Pokémon that he entrusted to Jessie, James and Meowth so they could defeat gym challengers while he was away from the Viridian City Gym. None of Rhydon's moves are known
Kingler is one of the Giovanni's Pokémon that he entrusted to Jessie, James and Meowth so they could defeat gym challengers while he was away from the Viridian City Gym.
Kingler's known moves are Crabhammer, Harden, and Bubble.
Machamp is one of the Giovanni's Pokémon that he entrusted to Jessie, James and Meowth so they could defeat gym challengers while he was away from the Viridian City Gym. Machamp's only known move is Karate Chop
Jessie received a Charizard from Delibird and used in a battle with James and his Aggron against Ash and Brock for control of Pewter City Gym. In the end it is revealed that Jessie and James got those Pokémon in error and that they were intended for Butch and Cassidy and therefore must be returned to Delibird.
Jessie's and James' English names derive from the notable outlaw Jesse James.
In Plant It Now... Diglett Later, an old woman says to Jessie that she is 120 years old and Jessie says that's 10 times her age, meaning that she is 12 years old. Because Jessie and James are described as idiotic, it could just be bad math on her part, or a typical case of a vain woman claiming to be younger than she really is, which would be within Jessie's character.
In some scenes Jessie is seen without lipstick. Most of these scenes were bloopers but few were on purpose. Examples would be of her as a child and when she was working out at the gym.
Despite her and James being major characters throughout the anime and manga, they have only appeared in the first Generation games.
Jessie is the only female main character to appear in all generations of the anime as Misty only appeared as a main character in 2 generations while May, Dawn, Iris and Serena have so far only appeared in 1 generation as a main character
In the official Cartoon Network site for Pokémon: BW Rival Destinies, it had a typo for Jessie that it did not have an "I" included in the character selection on the Title Header.